Chapter 9 Programming Languages

Have a vision of computer language evolution. Distinguish between machine, assembly, and high-level languages. Understand the process of creating and running a program. After reading this chapter, the reader should be able to: O BJECTIVES Distinguish between the different categories of languages: procedural, object-oriented, functional, declarative, and special. Become familiar with elements of the procedural language C.

EVOLUTIONEVOLUTION 9.1

Evolution of computer languages Computer language – a set of predefined words that are combined into a program according to predefined rules (syntax).

The only language understood by a computer is machine language. Note: Each computer has its own machine language, which is made of streams of 0s and 1s.

Program 9.1 Program in machine language

Symbolic language – simply mirrored the machine languages using symbols to represent the various machine language instructions. Assembler – a special program to translate symbolic code into machine language. Assembly language

Entry main,^m subl2 #12,sp jsb C$MAIN_ARGS movab $CHAR_STRING_CON pushal -8(fp) pushal (r2) calls #2,read pushal -12(fp) pushal 3(r2) calls #2,read mull3 -8(fp),-12(fp),- pushal 6(r2) calls #2,print clrl r0 ret Program 9.2 Program in symbolic language

High-Level language –  Portable to many different computers  Allow programmer to concentrate on application  Must be converted to machine languages (Compilation) Natural language – English, French, or Chinese

/* This program reads two integer numbers from the keyboard and prints their product. */ #include int main (void) { // Local Declarations int number1; int number2; int result; // Statements cin >> number1; cin >> number2; result = number1 * number2; cout << result; return 0; }// main Program 9.3 Program in C++ language

BUILDINGAPROGRAMBUILDINGAPROGRAM 9.2

Building a program 1. Writing and Editing 2. Compiling 3. Linking  Running 1. Load 2. Execute

Building a program Source file Object file Executable file Assemble all subprograms into final executable program

PROGRAMEXECUTIONPROGRAMEXECUTION 9.3

Program execution Loader – An OS program to load the program into memory for executing

CATEGORIESOFLANGUAGESCATEGORIESOFLANGUAGES 9.4

Categories of languages

Procedural language – a set of instructions that are executed one by one from beginning to end unless an instruction forces the control elsewhere. When programmers need to solve a problem, they should know the procedure to follow. For each problem, the programmer should carefully design an algorithm, and the algorithm should be carefully translated to instructions. Imperative language – each instruction is a command to the computer to do some specific task.

Fortran –  For scientific and engineering application  The first high-level language COBOL –  a business programming language Pascal –  Structured programming for teaching

C –  High-level instructions (Structured programming for writing UNIX)  Low-level instructions to access the hardware directly and quickly. Closer to assembly language than any other language. A good language for system programmers.  Efficient language; its instructions are short.  Standardized by ANSI and ISO

Procedural language –  Objects – independent from Operations  Objects – passive Object-Oriented language –  An approach to problem solving that is totally different from procedural language.  Objects – tied together with Operations  Objects – active

C++ -  Developed by Bell Lab.  adds object-oriented features to its predecessor, C. Java –  Developed by SUN, Based on C and C++  Java source code files are compiled into a format called bytecode, which can then be executed by a Java interpreter.  Compiled Java code can run on most computers because Java interpreters and runtime environments, known as Java Virtual Machines (VMs), exist for most operating systems.  Programs Application – a complete stand-alone program that can be run independently. Applet – embedded in HTML language, stored on a server, and run by a client browser.

Function in a functional language In Functional language, a program is considered a mathematical function. A function is a black box that maps a list of inputs to a list of outputs. LISP – designed by MIT

Extracting the third element of a list Rest – extracts all the elements except the first. First - extracts all the first elements.

HTML (Hypertext Markup Language)  A seudolanguage that includes marks that serve as formatting hints and links to other files.  An HTML file is made of text and tags. An HTML file (page) is stored on the server and can be download by a browser. Browser – removes the tags and interprets them as either formatting hints or links to other files.

Table 9.1 Common tags Meaning Meaning document document head document body document title different header levels boldface Italic underlined subscript superscript centered line break ordered list unordered list an item in the list an image an address (hyperlink) Beginning Tag Ending Tag

Sample Document This is the picture of a book: Program 9.4 HTML Program

Perl (Practical Extraction and Report Language)  a programming language especially designed for processing text.  one of the most popular languages for writing CGI scripts.  CGI (Common Gateway Interface) programs are the most common way for Web servers to interact dynamically with users. Many HTML pages that contain forms, for example, use a CGI program to process the form's data once it's submitted. SQL (Structured Query Language) – a language used to answer queries about database.

A PROCEDURAL LANGUAGE:C LANGUAGE:C 9.5

Variables Variables – names for memory locations. Each memory location has an address.  Used by the computer internally  Inconvenient for the programmer

Constants constants – data values that cannot be changed during the execution of a program.  Literal constant – a = 2 * p * r ;  Named constant – constant pi = 3.14;  Symbolic constant - #define taxRate

Table 9.2 Arithmetic operators Example Example  4 Num * 5 Sum / Count Count % Count ++ Count  Operator   *     Definition Addition Subtraction Multiplication Division (quotient) Division (remainder) Increment Decrement

Table 9.3 Relational operators Example Example Num1 < 5 Num1 <= 5 Num2 > 3 Num2 >= 3 Num1 == Num2 Num1 != Num2 Operator <     Definition Less than Less than or equal to Greater than Greater than or equal to Equal to Not equal to

Table 9.4 Logical operators Example Example ! ( Num1 < Num2 ) (Num1 10 ) Operator ! && Definition NOT AND OR

Table 9.5 Assignment operators Meaning Store 5 in Num Num = Num + 5 Num = Num  5 Num = Num * 5 Num = Num / 5 Num = Num % 5 Operator == +=  = *= /= %= Example Example Num = 5 Num += 5 Num  = 5 Num *= 5 Num /= 5 Num %= 5

label: goto label; Statement  cause an action to be performed by the program.  translates directly into one or more executable instructions.

Statement  Expression statement – a statement by placing a semicolon(;) after it. a++; b = 4; c = b + c * 4;  Compound statement – a unit of code consisting of zero or more statements. { x = 1; y = 20; }

Functions  In C, a subroutine is called a function.  A C program is made of one or more functions, one and only one of which must be called main.  The execution of the program always starts and ends with main, but this function can call other functions.  The function main is called by the operating system; main in turn calls other functions. When main is complete, control returns to the operating system.

Side effect of a function Side effect  Is an action that results in a change in the state of the program.  Occurs while the function is executing and before the function returns.  In general, the purpose of a function is At the same time, a function can have a side effect.

Parameter Passing  Pass by value  Pass by reference Function declaration Function header Function body Return type Formal parameters Actual parameters

Parameter Passing  Pass by value – a copy of data is created and placed in a local variable in the called function.  Pass by reference – sends the address of a variable to the called function rather than sending its value.

Call by Value void swap(int x, int y) { int temp; temp=x; x=y; y=temp; } ab y x 12 temp main() { int a=1,b=2; swap(a, b); } 12

Call by Address (Reference) void swap(int *x, int *y) { int temp; temp=*x; *x=*y; *y=temp; } ab y x 12 temp main() { int a=1,b=2; swap(&a, &b); } *x *y

if-else statement

switch statement

while loop

for loop False

do-while loop

Recursion C language supports recursion. A function in C can call itself. int fac(int n) { if (n == 0) return(1); else return( n * fact(n-1) ); }

Recursion C language supports recursion. A function in C can call itself. int fac(int n) { if (n == 0) return(1); else return( n * fac(n-1) ); }

The Towers of Hanoi It is a puzzle about three poles and n disks of increasing sizes. Initially, all the of the disks (all have holes at their centers) are placed on the first pole. Our goal is to transfer all the disks from the first pole to the third. We can move only one disk at a time and it is not allowed to place a larger disk on top of a smaller one. Let T(n) denote the number of moves. Then T(n) = 2T(n-1) + 1. Finally we get T(n) = 2 n - 1. A BC

Recursive solution Solve(n, A, B, C) { if (n == 1) A → C else { Solve(n-1, A, C, B) Move from A → C Solve(n-1, B, A, C) } } n A → C B n-1 A → B C n-1 B → C A A → C